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Digestive System – Part 1 Function of the Digestive System To convert foods into simpler molecules that can be absorbed and used by the cells of the body Parts of the Digestive System • The digestive system includes the mouth, pharynx, esophagus, stomach, small intestines and large intestines • Salivary glands, pancreas, gall bladder and liver add secretions to the digestive system Mouth Digestion begins at the mouth Teeth tear and crush food into smaller pieces. Mechanical Digestion (Chewing) Mechanical digestion is the physical breakdown of large pieces of foods into smaller pieces Teeth Teeth do most of the mechanical digestion by cutting, tearing, and crushing food into small fragments Teeth are anchored in the bones of the jaw Chemical Digestion As you chew your food, digestive enzymes begin the breakdown of food into smaller molecules Saliva As you chew, the salivary glands secrete saliva Saliva moistens food Contains the enzyme Amylase that breaks starches into smaller sugars YouTube The Digestive System STOP HERE! Digestive System – Part 2 Esophagus The tube that connects the mouth to the stomach Peristalsis Peristalsis - food is moved along the esophagus by contractions of smooth muscle Stomach Food from the esophagus empties into a large muscular sac called the stomach The stomach continues the mechanical and chemical digestion of food Chyme Chyme – semifluid, partially digested food that is expelled from the stomach to the duodenum Duodenum Duodenum The chyme enters the duodenum, the first part of the small intestine. The duodenum is where all of the digestive enzymes enter Jejunum Jejunum – second part of the small intestine Most of the nutrients in food are absorbed here Villi and Microvilli Villi and microvilli - the folded surface of the small intestine. Nutrient absorption occurs here YouTube The Digestive System STOP HERE! Digestive System – Part 3 ileum Ileum – third part of the small intestine Vitamin B12 and bile salts are absorbed here Large Intestine (colon) Water, cellulose and other undigested material enter the large intestine Primary function of the large intestine is to remove water from the undigested material Rectum Final section of the large intestine Temporary storage for feces Pancreas Pancreas – the gland that controls blood sugar levels Produces insulin and glucagon. Secretes digestive enzymes that break down food. Liver The liver produces bile, which acts like a detergent, dissolving and dispersing droplets of fat. Breaks down and detoxifies substances in the body Gall Bladder Stores bile produced by the liver and secretes it to the small intestine. STOP HERE! Large Intestine (colon) The material that leaves the small intestine is nutrient free Water, cellulose and other undigestible material enter the large intestine Primary function of the large intestine is to remove water from the undigested material The waste material that remains passes through the rectum and is eliminated from the body at the anus Bacteria in the large intestine produces vitamin K Accessory Structures of Digestion The pancreas produces enzymes that break down carbohydrates, proteins, lipids and nucleic acids. Gallbladder Liver The pancreas also produces sodium bicarbonate, a base that neutralizes stomach acid. The liver produces bile, which acts like a detergent, dissolving and dispersing droplets of fat. Bile is stored in the gallbladder. Duodenum Pancreas ileum The duodenum is much shorter than the remaining parts of the small intestine - the jejunum and ileum Much of the chemical digestion has been completed when the chyme reaches the jejunum The chyme is now a rich mixture of medium and small nutrient molecules Chemical & Mechanical Digestion in Stomach Chemical digestion - HCl and Pepsin begins the process of protein digestion. Mechanical digestion - Stomach muscles contract to churn and mix stomach fluids and food producing Chyme.